Diagnostic accuracy of Faecal Immunochemical Testing for patients with symptoms of colorectal cancer: a retrospective cohort study of 14,487 consecutive test requests from English primary care.

<jats:p>Objective: To ascertain the diagnostic performance of faecal immunochemical test (FIT) in symptomatic primary care patients, to provide objective data on which to base referral guidelines. Design: Stool samples from routine primary care practice in Oxfordshire, UK were analysed using the HM-JACKarc FIT method between March 2017 to March 2020. Clinical details described on the test request were recorded. Patients were followed up for up-to 36 months in linked hospital records for evidence of benign and serious (colorectal cancer, high-risk adenomas and bowel inflammation) colorectal disease. The diagnostic accuracy of FIT is reported by gender, age, and FIT threshold. Results: In 9,896 adult patients with at least 6 months of follow-up, a FIT result ≥10 ug/g had an overall sensitivity for colorectal cancer of 90.5% (95% CI 84.9%-96.1%), women 90.0 (80.7-99.3), men 90.8 (83.7-97.8); overall specificity 91.3 (90.8-91.9), women 92.4 (91.8-93.1), men 89.8 (88.8-90.7); overall Positive Predictive Value (PPV) 10.1 (8.15-12.0), women 7.64 (5.24-10.0), men 12.5 (9.52-15.5)); and an overall Negative Predictive Value (NPV) 99.9 (99.8-100.0), women 99.8 (99.7-100.), men 99.9 (99.9-100.0). The PPV and specificity of FIT were higher for serious colorectal disease combined and the sensitivity and NPV were lower than for colorectal cancer alone. The Area Under the Curve (AUC) for all patients did not change substantially by increasing the minimum age of testing. In this population, 10% would be further investigated to detect 91% of the cancers at 10ug/g and 3% further investigated to detect 54% of the cancers at 150ug/g. The number needed to scope to detect one cancer at was ten using FIT at 10ug/g. Conclusion: A FIT threshold of 10ug/g is appropriate to triage adult patients presenting to primary care with symptoms of serious colorectal disease. FIT may provide an appropriate approach to reprioritising patients colorectal cancer symptoms whose tests have been delayed by the COVID-19 pandemic.</jats:p>